1021 - Cervical Histology Flashcards
How do normal cells appear on cytology? Neoplastic cells?
Flat or orderly sheets.
Nuclei are fairly small (with low N:C ratio), similar in appearance, smooth, not dark, and chromatin is fine and evenly distributed.
Neoplastic - Cells overlap one another, disorganised.
Nuclei are too big, variable in size and shape (raisinoid and high N:C ratio), dark coloured with irregular outline.
What does metaplasia mean? Example?
A change in the growth of tissue, often in response to an environmental factor.
As cervical columnar cells are everted into the vagina, they can become metaplastic, with squamous cells developing. This metaplasia places the cells at risk for neoplasia/cervical cancer.
How does histology change over the length of the cervix?
Endocervix consists of columnar epithelium. There is a well-deliniated squamo-columnar junction and a defined transformation zone of metaplastic squamous epithelium. Mature ‘basket weave’ squamous epithelium also exists.
Outline the CIN classifications
Cervical Intraepithelial Neoplasia
CIN1 - Mild dysplasia in basal ⅓ of epithelium. Consistent with HPV infection, and can be cleared by immune system.
CIN2 - Moderate dysplasia in basal ⅔ of epithelium.
CIN3 - Severe dysplasia, possibly across entire epithelium - cervical carcinoma in situ.
What Percentage of cervical carcinomas are associated with HPV infection? What types of HPV are most carcinogenic?
90%
Type 16 accounts for 55% of cervical cancer, type 18 for 13%.
What is the aim of cervical screening?
Prompt and efficient identification and ablation of significant precursor lesions (CIN2/3) to SCC or adenocarcinoma.
What are the 10 key principles of screening?
Condition should be an important health problem.
Accepted treatment for patients with the disease
Facilities for diagnosis and treatment should be available
Should be a suitable test or examination
Test must be acceptable to the population
Good understanding of progression of disease
Agreed policy on whom to treat
Funding should be balanced in relation to overall health expenditure
Case-finding should be a continuing process, not a one-off project.
What is sensitivity?
Probability that a test will be a true positive in a person with the disease
a/(a+c)
A highly sensitive test is valuable in confirming that someone is free of disease if the test is negative (SnNout)
What is specificity?
Probability will be a true negative in a person who does not have the disease.
d/(b+d)
A highly specific test is valuable in confirming that someone has the disease if the test is positive (SpPin).
What is positive predictive value?
The probability that a person with a positive test has the disease (a/a+b) - takes into account the prevalence of the disease in a population (false positives will still be a constant rate, but true positives will change based on prevalence).
What is negative predictive value?
Probabilty that a person with a negative test does not have the disease (D/C+D). Takes into account the prevalence of the disease in a population (false negatives will still be a constant rate, but true negatives will change based on prevalence).
